actually observe ML_system_unsafe, concerning the environment that is stored in theory ML_Root;

--- a/src/Pure/ROOT.ML	Tue Apr 05 18:20:25 2016 +0200
+++ b/src/Pure/ROOT.ML	Tue Apr 05 18:25:42 2016 +0200
@@ -335,6 +335,6 @@
 use "Tools/jedit.ML";
 
 use_thy "Pure";
-use_thy "ML/ML_Root";
 
 use "ML/ml_pervasive_final.ML";
+use_thy "ML/ML_Root";